The ultimate aim of these studies is to develop potent antiestrogens capable of controlling growth of estrogen-dependent tumors in humans by non-invasive endocrine therapy. Because of their known specific interaction with estrogen receptors, antiestrogens seem particularly well suited to be specific, antitumor agents in the cases of estrogen dependent tumors, theoretically capable of achieving non-surgical endocrine therapy. Our studies will assess the interaction of antiestrogens with estrogen receptors in target tissues and their in vivo pharmacokinetic behavior.